The present invention relates to a helicopter blade longitudinal member.
Generally speaking, all known helicopter blades comprise an axial load-bearing element, consisting of a longitudinal member forming the front part of the blade, i.e. the part next to the leading edge, and a rear fairing made integral with the rear edge of the longitudinal member.
Known longitudinal members are made using a wide variety of materials, though the recent tendency has been increasingly towards the use of synthetic composite materials.
Known composite longitudinal members are usually tubular in shape and made by curing in a mold, usually starting from a number of axial straps made of uncured synthetic composite material. The straps are arranged over a removable inner core on mold and then covered with an outer covering of synthetic material which, when cured, becomes one with the straps and with any inner covering contacting the core.
Forming a composite longitudinal member of the aforementioned type is not always an easy job in that, on the one hand, the shape stability of the uncured straps is practically nil and, on the other hand, any gaps left in the uncured material inside the mold result either in surface defects or internal air pockets, which usually result in the longitudinal member being rejected.
The standard procedure for overcoming this drawback has been the definition of complicated forming procedures, usually involving manual compacting of the uncured elements placed one after another inside the mold. Though providing for fairly good results, such procedures not only involve considerable cost, but depend too highly on the skill and experience of the maker.